Facebook Page Tab Authentication/Tracking

I'm creating a custom Facebook Page tab using HTML/PHP. The page tab will feature a link to download a PDF file. I want to be able to track who downloaded that file. I believe the page tab will need to authenticate the users in order for me to track who downloaded the file. That is the part I need you to do. Please let me know if you're interested.

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To,
The Employer,
Dear Sir / Madam:
Please accept this as my letter of application and supporting material for this position with your organization. I am very excited about this oppoLisää